Input and Output

Input and Output

Objectives

• Survey IO facilities in .NET Framework Class Library

– file and directory management – text files – binary files – object serialization

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IO Library

•

Input/output library in System.IO namespace

• Support provided for:

– file and directory management – text files – binary files – simple type conversion to/from binary

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Files and directories

• Two primary classes to work with files and directories

– perform file system interaction – generally do not manipulate file contents – derived from common base

FileSystemInfo

DirectoryInfo

FileInfo

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FileSystemInfo

• Files and directories have some operations in common

– provided in base class FileSystemInfo

name

public abstract class FileSystemInfo ... {

characteristics

public abstract string Name { get; } public string FullName { get; } public string Extension { get; }

delete

{ get; } public abstract bool Exists public DateTime CreationTime { get; set; } public DateTime LastAccessTime { get; set; } public DateTime LastWriteTime { get; set; } { get; set; } public FileAttributes Attributes

public void Delete() ... ...

}

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DirectoryInfo

• DirectoryInfo represents a directory

– methods provided to examine and manipulate – inherits common operations from FileSystemInfo

public sealed class DirectoryInfo : FileSystemInfo {

public DirectoryInfo(string path) ... constructor

navigation public DirectoryInfo Parent { get; } { get; } public DirectoryInfo Root

manipulation

() ... public void Create (string destDirName) ... public void MoveTo (bool recursive ) ... public void Delete public DirectoryInfo CreateSubdirectory(string path ) ...

contents

() ... public FileInfo [] GetFiles public DirectoryInfo [] GetDirectories () ... public FileSystemInfo[] GetFileSystemInfos() ... ...

}

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FileInfo

• FileInfo represents a file

– methods provided to examine and manipulate – inherits common operations from FileSystemInfo

public sealed class FileInfo : FileSystemInfo {

public FileInfo(string fileName) ... constructor

public long Length { get; } length

location public string DirectoryName { get; } public DirectoryInfo Directory { get; }

manipulation

public FileInfo CopyTo(string destFileName) ... public FileInfo CopyTo(string destFileName, bool overwrite) ... public void MoveTo(string destFileName) ... ...

}

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Application: List contents

• Can examine contents of a directory

void List(string path) {

DirectoryInfo directory = new DirectoryInfo(path);

contents

FileInfo [] files = directory.GetFiles (); DirectoryInfo[] directories = directory.GetDirectories();

files

foreach (FileInfo f in files) Console.WriteLine(f.Name);

directories

foreach (DirectoryInfo d in directories)

Console.WriteLine(d.Name);

}

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Application: Find file

• Can search file system to find specified files

void Find(string filename, DirectoryInfo root, ArrayList results) {

foreach (FileInfo f in root.GetFiles(filename)) search with pattern results.Add(f.FullName);

foreach (DirectoryInfo d in root.GetDirectories())

Find(filename, d, results); recursive call for each subdirectory

}

DirectoryInfo root = new DirectoryInfo(@"C:\WINDOWS"); ArrayList results = new ArrayList();

Find("mscoree.dll", root, results);

foreach (string s in results)

Console.WriteLine(s);

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Utility classes

• Three utility classes also work with files and directories

– Path – Directory – File

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Path

• Path provides static methods to manipulate a path string

– most do not interact with the file system

public sealed class Path {

public static bool HasExtension (string path) ... public static string GetExtension (string path) ... public static string ChangeExtension(string path, string extension) ...

public static string GetDirectoryName(string path) ...

public static string GetFileName (string path) ... public static string GetFileNameWithoutExtension(string path) ...

public static readonly char DirectorySeparatorChar; public static readonly char VolumeSeparatorChar; public static readonly char PathSeparator; ...

}

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Application: parse path

• Path methods useful to parse path into constituent parts

public void Parse(string path) { C:\WINDOWS\system32 string a = Path.GetDirectoryName (path);

mscoree.dll string b = Path.GetFileName (path);

mscoree string c = Path.GetFileNameWithoutExtension(path);

.dll string d = Path.GetExtension (path);

C:\ string e = Path.GetPathRoot (path);

...

}

string path = @"C:\WINDOWS\system32\mscoree.dll";

Parse(path);

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Directory

• Directory has static methods to manipulate directories

– most have analogues in DirectoryInfo – several offer unique functionality

public sealed class Directory {

public static string[] GetLogicalDrives() all drives on system

current directory public static string GetCurrentDirectory() public static void SetCurrentDirectory(string path)

similar methods in DirectoryInfo

public static bool Exists (string path) ... public static string[] GetFiles (string path) ... public static string[] GetDirectories(string path) ... public static void Delete (string path) public static void Move(string source, string dest) ...

}

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Application: examine drives

• Can examine all logical drives

– use Directory.GetLogicalDrives to get drives – use Directory.Exists to determine if disk in drive

all drives

string[] drives = Directory.GetLogicalDrives();

foreach (string s in drives) {

disk in drive?

if (Directory.Exists(s))

...

}

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File

• File has static methods to manipulate files

– all have analogues in FileInfo

public sealed class File {

similar methods in FileInfo

public static bool Exists(string path) ... public static void Delete(string path) ... public static void Copy (string source, string dest) ... public static void Move (string source, string dest) ... ...

}

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Choice of file / directory class

• Must sometimes decide which class to use

– File vs. FileInfo – Directory vs. DirectoryInfo

• Static methods

•

– can offer more convenient usage syntax – require permission check on each call Instance methods – must instantiate object – some permission checks can be done once in constructor

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File contents manipulation

• Classes provided to manipulate file contents – separate classes for text and binary files – filters convert simple types to/from bytes for binary storage – support for disk or memory files

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Character IO

• Classes provided to do character IO

– most methods defined in base classes – derived classes specialized for data location and operation

TextReader

TextWriter

StreamReader

StringReader

StreamWriter

StringWriter

write to disk

read from disk

write to StringBuilder

read from string

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StreamWriter

• StreamWriter writes characters to text file – open file with one of many constructors – write with overloaded Write / WriteLine methods – close

text file

automatically converted to string using ToString

open

char, bool, string, short, int, long, float, double, etc.

StreamWriter sw = new StreamWriter("Chores.txt"); int n = 3;

write

sw.WriteLine("Go to pet store"); sw.Write("Feed all "); sw.Write(n); sw.WriteLine(" cats");

sw.Close();

close

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StreamReader

• StreamReader reads characters from text file – open file with one of many constructors – read characters or strings with Read / ReadLine methods – close

text file

open

can read only char or string char, string

StreamReader sr = new StreamReader("Chores.txt"); string s;

read

while ((s = sr.ReadLine()) != null)

Console.WriteLine(s);

close

sr.Close();

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Byte IO

• Classes provided to do byte IO

– most methods defined in base class

• Two possible data locations provided in System.IO

– disk – memory

Stream

FileStream

MemoryStream

read/write disk

read/write byte array

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Stream methods

• Stream offers extensive functionality

– read / write bytes – random access – asynchronous read / write

public abstract class Stream ... {

read/write

public virtual int ReadByte () ... public virtual void WriteByte(byte value) ... public abstract int Read (byte[] buffer, int offset, int count); public abstract void Write(byte[] buffer, int offset, int count);

(long offset, SeekOrigin origin);

public abstract long Seek public abstract long Position { get; set; } random access

asynch

public virtual IAsyncResult BeginRead (...) ... (...) ... public virtual int EndRead public virtual IAsyncResult BeginWrite(...) ... public virtual void EndWrite (...) ... ...

}

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FileStream

• FileStream supports read / write bytes to disk file

open

FileStream f = new FileStream

(

"Bytes.dat", FileMode.Create, FileAccess.ReadWrite

binary file

);

write

byte, byte[]

back up 2 bytes

f.WriteByte((byte)10); f.WriteByte((byte)20); f.WriteByte((byte)30); f.WriteByte((byte)90); f.WriteByte((byte)50);

back up to beginning

f.Seek(-2, SeekOrigin.Current); f.WriteByte((byte)40);

f.Seek(0, SeekOrigin.Begin); int b = f.ReadByte();

close

f.Close();

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Simple type output

• BinaryWriter converts many core types to binary

– must be used with a stream for storage – Write methods convert and write bytes to backing stream

converter

binary file

simple types bytes

char, bool, string, short, int, long, float, double, etc.

data store FileStream data = new FileStream("Bytes.dat", FileMode.Create);

converter BinaryWriter converter = new BinaryWriter(data);

write

converter.Write(17); converter.Write(3.14); converter.Write("hello");

converter.Close(); close both streams

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Simple type input

• BinaryReader reconstructs types from binary – must be given a stream containing bytes – Read methods read from backing stream and convert

converter

binary file

simple types bytes

char, bool, string, short, int, long, float, double, etc.

data store FileStream data = new FileStream("Bytes.dat", FileMode.Open);

converter BinaryReader converter = new BinaryReader(data);

read

int i = converter.ReadInt32 (); double d = converter.ReadDouble(); string s = converter.ReadString();

converter.Close(); close both streams

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Serialization

• Can save/restore state of object to stream

– called serialization

Point x=1, y=2 ...

save serialize

x 1 y 2

Point x=1, y=2 ...

restore deserialize

x 1 y 2

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Serializable attribute

• Type author must explicitly allow serialization – tag with Serializable attribute to allow – otherwise get SerializationException

allow points to be serialized

[Serializable] class Point {

int x; int y; ...

}

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Formatter

• BinaryFormatter used to serialize/deserialize object

– in namespace

System.Runtime.Serialization.Formatters.Binary

public sealed class BinaryFormatter ... {

save object to stream

public void Serialize(Stream destination, object o) {

...

}

restore object from stream

public object Deserialize(Stream source) {

...

} ...

}

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Save

• Use Serialize method to save object to stream

void Write() {

FileStream dest = new FileStream("MyData.dat", FileMode.Create);

Point data = new Point(1, 2);

BinaryFormatter formatter = new BinaryFormatter();

formatter.Serialize(dest, data);

...

}

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Restore

• Use Deserialize method to restore object from stream

– return type is object, typical to downcast

void Read() {

FileStream source = new FileStream("MyData.dat", FileMode.Open);

BinaryFormatter formatter = new BinaryFormatter();

Point data = (Point)formatter.Deserialize(source); ...

}

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Object graph

• Serialization preserves object graph – all referenced objects are serialized – graph rebuilt when deserialized

x 1 y 2

c

center radius 3

Both circle and center point would be serialized

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Summary

•

IO facilities provided by .NET Framework class library – in System.IO namespace

• Can manipulate files and directories • Can read/write file contents

– characters – bytes

• Can convert simple types to/from binary format • Serialization allows objects to be read/written to stream

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